1 - Hypofractionated vs. Conventional Fractionated Postmastectomy Radiotherapy in High-Risk Breast Cancer: 10-Year Outcomes from a Phase 3 Randomized Trial

01:30pm - 01:39pm ET

Grand Ballroom

Presenter(s)

Guang-Yi Sun, MD - National Cancer Center/Cancer Hospital, Chinese Academy of Medical Science and Peking Union Medical, Beijing, Beijing

G. Y. Sun¹, S. Y. Chen¹, T. Yu¹, H. Fang¹, Y. W. Song¹, Y. Liu¹, J. Jin², N. Li¹, N. Lu¹, Y. Tang¹, S. Qi¹, B. Chen¹, H. Jing¹, Y. Zhai¹, W. Zhang¹, X. Liu¹, Z. Yang¹, X. Zhao¹, Y. Song¹, D. Q. Wang¹, S. J. Wang¹, Z. Qiu¹, Z. Chaonan¹, S. J. Yang¹, J. R. Zhu¹, J. R. Liu¹, X. Shen¹, C. Hu³, Y. X. Li¹, and S. Wang¹; ¹Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ²State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, ³Division of Biostatistics and Bioinformatics, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD

Purpose/Objective(s):

Hypofractionated radiotherapy is an established alternative to conventional fractionation for breast cancer, but long-term evidence supporting its use after mastectomy with regional nodal irradiation remains limited. The CHN HYPOPMRT trial previously demonstrated non-inferiority of hypofractionated postmastectomy radiotherapy at 5 years. We report the 10-year outcomes to assess durability of tumor control and late safety.

Materials/Methods:

In this open-label, phase 3, randomized, non-inferiority trial conducted at a national cancer center in China, women with high-risk breast cancer who had undergone mastectomy and axillary dissection were randomly assigned (1:1) to receive conventional fractionated radiotherapy (50 Gy in 25 fractions over 5 weeks) or hypofractionated radiotherapy (43·5 Gy in 15 fractions over 3 weeks) to the chest wall and supraclavicular region. The primary endpoint was 5-year cumulative incidence of locoregional recurrence. Long-term outcomes through 10 years were analyzed descriptively. Secondary endpoints included disease-free survival, overall survival, and late radiation-related toxicities.

Results:

Between June 2008 and June 2016, 820 patients were enrolled; 810 were included in the modified intention-to-treat analysis (409 conventional fractionation, 401 hypofractionation). At a median follow-up of 11.5 years (interquartile range 9.6 to 13.8), the cumulative incidence of locoregional recurrence at 5 years was 8.6% in the conventional fractionation group and 9.6% in the hypofractionation group (hazard ratio 1.13, 90% confidence interval 0.77 to 1.66; 95% confidence interval 0.72 to 1.79). At 10 years, locoregional recurrence remained similar between groups (10.3% versus 12.0%; hazard ratio 1.19, 95% confidence interval 0.79 to 1.82). For secondary endpoints, no significant differences were observed at 10 years in disease-free survival (65.2% versus 69.9%) or overall survival (72.9% versus 77.5%). No grade 4–5 late toxicities or cases of brachial plexopathy were observed. Grade 1–2 pulmonary fibrosis was more frequent with hypofractionation. (19.7% versus 11.7%; p=0.008).

Conclusion:

Hypofractionated postmastectomy radiotherapy provides durable locoregional control, comparable survival outcomes, and acceptable long-term toxicity in high-risk breast cancer. These findings support hypofractionation as a safe and efficient alternative to conventional fractionation in this setting. This trial is registered at ClinicalTrials.gov, number NCT00793962.